The invention relates to compositions which inhibit microbial infection. Microbes include parasites such as Acanthamoeba castellanii, A. culbertsoni, A. hatchetti, A. polyphagia, A. rhysodes, Entamoeba histolytica, Giardia lamblia, Leishmania amazomen, and Trypanosoma cruzi; and bacteria such as Pseudomonas aeruginosa. Acanthamoeba are present in soil, air, swimming pools, hot tubs, tap water, and contact-lens care products. Individuals who are susceptible to opportunistic pathogens such as Acanthamoeba include those who are chronically ill, immunocompromised, pregnant, diabetic, or suffer from liver disease or alcoholism. Immunocompromised individuals include patients with lymphoma, leukemia, or AIDS, and those taking immuno-suppressive medication such as organ transplant patients. Acanthamoeba infections include granulomatous amebic encephalitis and cutaneous lesions. In immunocompetent individuals, Acanthamoeba cause a vision-threatening corneal infection known as Acanthamoeba keratitis. Many patients with Acanthamoeba keratitis are contact lens wearers. Current therapy includes the use of Brolene and neomycin, or clotrimazole.